1. Field of the Invention
The present invention relates to an implantable, calibrateable measuring instrument for a body substance and a calibrating method therefor, and in particular to such an instrument which can be used for controlling an implantable infusion device, for example an insulin infusion device.
2. Description of the Prior Art
Instruments are known for measuring a body substance which can be implanted together with an infusion device for controlling the medication dose to the patient. It is also known to equip such instruments with a calibration means so that periodic adjustment of the instrument can be made, if necessary.
Ideally, control of an implanted medication dosing device is made with a co-implanted measuring instrument which monitors the body parameter to be controlled via a measuring sensor. A control signal for the metering pump in the infusion device is derived from the electronically processed measured signal. An example of such a device is known from diabetes therapy. In such devices, the measured variable and the controlled parameter are the glucose concentration in the body, for example, in the blood, the connecting tissue, or the peritoneum of the patient. The controlled variable is the insulin conveying rate. In such a device, known as a closed-loop device, the measuring sensor is usually subject to drift. Such drift can be associated with the zero point, the slope of the processed signal, or the shape of the processed signal, thus requiring periodic calibration.